Parents will face prosecution for all but the gentlest smacks under proposals passed overwhelmingly by Britain's House of Lords yesterday.
They could be jailed and banned from working with youngsters merely for delivering a slap which caused the skin to redden.
The dramatic clampdown on the rights of parents to discipline their children, backed by Prime Minister Tony Blair, is seen by critics as a "snooper's charter".
It is the first step towards parents being reported and prosecuted if they cause "actual bodily harm" by smacking children.
The Attorney-General Lord Goldsmith told peers that actual bodily harm would include grazes, minor bruising, superficial cuts, abrasions or even "psychological" injury.
The ban was approved by 226 votes to 91 after Mr Blair threw his weight behind it and gave Labour peers a free vote on the question.
The Commons is expected to back the ban. Labour MPs also will be given a free vote when they debate the issue in the autumn and it is likely to become law by the end of the year.
The drastic restriction raises the spectre of parents being criminalised simply for disciplining their children if it inadvertently causes injury. They face investigation by police and social workers if anyone, even a complete stranger, chooses to complain about their behaviour.
However, peers rejected a total smacking ban, which would have outlawed even the gentlest slap on the wrist, by 250 votes to 75.
Liberal Democrat peer Lord Lester said the law should no longer protect parents who left their children bruised or cut.
He was supported by Lord Laming, who chaired the inquiry into the murder of eight-year-old Victoria Climbie which sparked the debate. Victoria died from hypothermia after she was entrusted to the care of her aunt Marie Therese Kouao. Downing street said Mr Blair opposed a total ban because he did not want to criminalise parents.
Meanwhile, Scotland has rejected a law that would have banned parents from smacking children under the age of three.